In recent years, the demand for high-capacity high-speed data transmission and reception has been increasing, and various studies are being undertaken to transmit and receive larger volumes of data at higher speeds. For example, to amalgamate electronics, which uses electronic devices such as field effect transistors, and photonics, which uses photonic devices such as light emitting diodes, signal processing techniques in the THz band which is in a higher frequency range than the millimeter wave band are being studied vigorously. To realize such techniques, electronic devices capable of operating in the THz band are indispensable.
Of the electronic devices, transistors which perform amplification, e.g., MOS transistors, have a gate insulator and thus have input impedance. When the operating frequency is increased, this input impedance causes an input's output to be delayed, and at frequencies higher than a certain level, the output waveform is distorted or amplification cannot be performed. Currently, development of electronic devices is being done under a strategy in which in order to increase the frequency (i.e., the cutoff frequency) at which current gain is 1, electronic circuits are miniaturized and materials having high electron mobility are used.
In Non-Patent Document 1, a transistor fabricated under this strategy is reported. This transistor is made of InGaAs, the gate length thereof is 25 nm, and, as a result, the cutoff frequency thereof is 0.562 THz.
Patent Document 1 also discloses a field effect transistor which includes a gate and a channel layer of two-dimensional electrons, and in which a high cutoff frequency and a high gain are achieved at a high frequency by applying a magnetic filed in a direction perpendicular to the direction in which the electrons flowing in the two-dimensional electron channel layer move. Patent Document 1 shows that when the gate length was 0.15 μm, a cutoff frequency of 1.08 THz was achieved.
Patent Document 1: Japanese Laid-Open Publication No. 2004-235568
Patent Document 2: Japanese Laid-Open Publication No. 5-226635
Non-Patent Document 1: K. Shinohara, et al., Jpn. J. Appl. Phys. 41, L437 (2002)
Non-Patent Document 2: T. Enoki, et al., Int. J. High Speed Electron. Syst. 11, 137 (2001)
Non-Patent Document 3: M. J. W. Rodwell, et al., IEEE Trans. Electron Devices 48, 2606 (2001)